While fiber based filter elements are well-known and have been used in the cigarette manufacturing field for at least 40 years, the choice of fiber-candidates for such filters has remained quite limited over the years, due to cost factors and lack of general suitabillity of many natural fibers for high speed production using art recognized filter rod-making apparatus. In addition, the functional demands on filter elements in the market place are strongly conflicting with respect to characteristics such as pressure drop, filter efficiency, resiliency and hardness.
While various synthetic fiber and fiber mixtures have been tried and evaluated in the market place, the largest number of cigarette filter elements continue to include cellulose acetate-based fibers.
Although cellulose acetate fiber filter elements are generally not as efficient as elements containing finer denier synthetic fibers such as polyolefins or mixtures thereof, there remain substantial cost and handling advantages in using such fiber filter elements. For example, cellulose acetate tow is relatively inexpensive and can be easily and rapidly processed into cuttable filter rods using commercial, state-of-the-art filter rod-making apparatus without causing serious jamming problems. This advantage is enjoyed despite the normal application of substantial amounts of non-volatile liquid organic plasticizers such as triacetin, diacetin, citric acid and the like onto garniture feed such as fiber tows. For such purpose, plasticizers are usually dipped or sprayed onto the open moving fiber tow, the droplets being absorbed to form random softened areas capable of adhering to adjacent fibers. Such bonding of randomly-arranged fibers through use of plasticizer is intended to impart sufficient rigidity to the resulting filter rod to permit high speed cutting to obtain unwarped filter tip-length elements.
The above-stated advantages of cellulose acetate fiber, however, are countered by several disadvantages. For example, cellulose acetate fibers are weak (1.0-1.2 g./denier) compared with synthetic fibers such as polyolefins. This characteristic seriously limits the amount of tension and/or crimp which can be applied to the fiber tow feed prior to introduction into a filter rod-making apparatus.
Synthetic fibers, particularly polyolefins such as polypropylene, as noted above, are easily drawn to a much smaller denier, offering improved filter efficiency without simultaneous loss of strength needed for crimping and high speed production. Such fibers, however, also have disadvantages. These stem mainly from the fact that a substrate, such as an open or bloomed tow is relatively inert and not readily wetted or softened by most adhesive/plasticizer or other hydrophilic-type modifier formulations.
Another substantial problem, unique to the cigarette fiber filter art, concerns a recognized difficulty in optimizing fiber denier, filter element efficiency and pressure drop without corresponding sacrifice in dimensional stability, resiliency and hardness of the resulting filter element. In particular, polyolefin fiber-containing substrates (i.e. particularly tows and slivers) fed into a filter rod-making apparatus have demonstrated a significant negative correlation between pressure drop (resistance to draw) and dimensional stability or hardness of the filter element. In addition, it is often very difficult to avoid jamming of heavily impregnated polyolefin or other synthetic substrates fed at high speed into a conventional filter rod-making apparatus, particularly substrates containing substantial amounts of modifier components such as adhesives, humectants, flavors, medicines, absorbents, adsorbents, and the like, into or onto the garniture feed. This is due, in part, to an inherent deficiency in lubricating properties of many additive compositions used in the cigarette filter art.
It is an object of the present invention to efficiently and precisely disseminate and fix active modifier components or compositions within cigarette filter elements for control and selective removal of certain toxic by-products normally within cigarette smoke.
It is a further object of the present invention to selectively remove or control the concentration of one or more toxic gas components within cigarette smoke.
It is a still further object of the present invention to control the concentration of hydrogen cyanide and nitrogen oxide within cigarette smoke through use of pretreated substrate(s) suitable as a high speed garniture feed for a conventional filter rod-making apparatus.